This invention was made in the course of, or under, a contract with the Energy Research and Development Administration.
Ion-induced radiation damage studies are often used to simulate neutron radiation damage such as described in the application of Everett E. Bloom et al., Ser. No. 596,546(70), filed July 16, 1975, and having a common assignee with the present application. These studies are among the most important of present charged-particle accelerator applications.
A common requirement of many of the irradiation studies concerns the fact that specimens are generally examined over a very small area, and often several specimens are irradiated simultaneously. It is therefore convenient to work with a beam having a very uniform beam density profile. Instead of having a uniform density, however, the typical beam from an ion accelerator has a more gaussian density profile; i.e., intense along the axis and trailing off gradually to zero intensity at the beam boundaries.
To achieve uniform impingment density on the target (specimen), the ions can be focused to a small spot and the beam rastered over the entire target array. Unfortunately, such a technique introduces an undesirable time dependence. An allowed procedure, but an inefficient one, is to place the target out so far along the axis as to accept only the central part of the divergent beam.
Accordingly, a need exists to provide a special focusing lens having as its primary object to concentrate the flux of a gaussian or nearly gaussian ion beam to a nearly uniform distribution onto a target. The present invention was conceived to meet this need in a manner to be described hereinbelow.